A conventional wireless network includes a set of access points (APs), (also known as base stations), each of which is connected to a backhaul network. In certain deployments, the cost of directly connecting a given AP to the backhaul network is too high. Thus, indirectly connecting the AP to the backhaul network may be more attractive. This indirect connection is typically accomplished by relaying information to and from neighboring APs in a mesh network. This is referred to as a mesh architecture.
A mesh network is a local area network (LAN) including a plurality of mesh points (MPs). The connections between the MPs may be wired or wireless. The points of interconnection between a mesh system and a non-mesh system are referred to as portals. A mesh system with multiple portals is referred to as a multi-portal mesh system. A node capable of both AP and MP functionalities is referred to as a mesh access point (MAP). FIG. 1 shows an exemplary mesh network 100. The mesh network 100 includes a plurality of MPs 102, a plurality of MAPs 104 and a mesh portal 106. The MPs 102 serve as forwarding and relaying nodes in the mesh network 100. The MPs 102 receive traffic on incoming links and forward the traffic on outgoing links. The MAPs 104 are also MPs with an interface to provide radio access to a plurality of wireless transmit/receive units (WTRUs) 108 to provide wireless services in a certain geographic area. The mesh portal 106 provides connectivity to a backbone network 110, (such as the Internet), in the mesh network 100. Thus, the mesh portal 106 acts as an MP with a special interface to the backbone network 110. Each of the WTRUs 108 communicates with another WTRU in the mesh network 100, or to the backbone network 110, via the MAPs 104 and the mesh portal 106. The MAPs 104 forward the traffic generated by the WTRUs 108 to another MAP 104 or the mesh portal 106 by relaying the traffic via intermittent MPs 102 and/or MAPs 104.
A mesh network is reliable and offers redundancy. Even if one or more of the MPs can no longer operate, the rest of the MPs can still communicate with each other, directly or through one or more intermediate MPs such that the network may function properly. Other considerations, such as ease and speed of deployment, are advantages of the mesh network since a mesh network may be deployed without having to provide direct backhaul links and interconnection modules for each MP in the mesh network.
In conventional non-mesh wireless communication systems, a WTRU needs to estimate which AP will provide the best communication link to the WTRU. WTRUs typically use the following information and methods for determining which AP to associate with:
1) the identity of the network of which a candidate AP is a part of, (e.g., in IEEE 802.11 systems, this identity corresponds to the service set identifier (SSID) provided to the WTRUs in a beacon frame or a probe response frame);
2) the capabilities of the candidate AP including information regarding which services the AP supports, (e.g., in IEEE 802.11 systems, this capability information is included in a capability information field in a beacon frame or a probe response frame); or
3) the expected achievable data throughput, (e.g., the WTRU may estimate the expected throughput by measuring a received power it perceives from an AP on beacon frames, probe response frames or any other frames). The received power, a signal-to-interference-plus-noise-ratio (SINR) or similar measurements typically sets the maximum rate the WTRU may achieve on a given communication link. The WTRU can also use channel occupancy or channel load measurements, whether measured by the WTRU or collected from the AP, to refine the expected throughput estimate.
The above-described information and methods utilized to select an AP that a WTRU should associate with are no longer adequate in a mesh network. For example, in a conventional infrastructure mode WLAN, the throughput achieved on a given WTRU-AP link depends only on the characteristics of that particular radio link between the AP and the WTRU, (i.e., channel occupancy, received power, a signal-to-interference and noise ratio (SINR), or the like). However, in a mesh network, the throughput not only depends on the characteristics of the radio link between a given WTRU and its serving MAP, but it also depends on the characteristics of the radio link(s) between the serving MAP and other intermediate MPs that forward the traffic from the serving MAP to the mesh portal.
FIG. 2 illustrates an example of an intelligent association problem in a conventional mesh network 200. In this example, the mesh network 200 comprises three MAPs 201, 202 and 203. The MAPs 201 and 203 are mesh portals which have connectivity to the Internet 230 via a router 220. The interconnection resources of the MAPs 201, 203 may be Ethernet-based. In this example, the MAP 202 and the MAP 203 are candidate MAPs for a WTRU 210. If the WTRU 210 is associated with the MAP 102, traffic to/from the Internet 230 is routed via radio links L2 and L1 via the MAP 201. If the WTRU 210 is associated with the MAP 203, the traffic to/from the Internet 230 is routed via radio link L3. An exemplary set of radio link characteristics for the radio links L1, L2 and L3 is illustrated in Table 1 below.
TABLE 1TransmissionSingle-linkRadio linkNodesSNRratethroughputL1MAP1MAP210 dB12 Mbps 5 MbpsL2STAMAP235 dB54 Mbps20 MbpsL3STAMAP320 dB36 Mbps15 Mbps
According to Table 1, if the WTRU 210 associates with the MAP 203, the throughput would be 15 Mbps. However, if the WTRU 210 associates with the MAP 202, the throughput would be determined by the combination of data throughput of two links L1, L2, which is typically estimated as follows:1/(1/throughput_L1+1/throughput_L2).  Equation (1)
Applying Equation (1) to radio links L1 and L2, the combined throughput would be 1/(1/5+1/20) or 4 Mbps. From this calculation it becomes evident that the WTRU 210 will experience a better throughput by associating with the MAP 203 than by associating with the MAP 202. From the perspective of the overall mesh network 200, the preferred association of the WTRU 210 is to the MAP 203. The radio connection of L1 and L2 between the WTRU 210 and the MAP 201 offers 3.75 times (i.e. 15 Mbps/4 Mbps) less throughput than the multi-hop radio connection between the WTRU 210 and the MAP 203.
According to the prior art, in the foregoing example, the radio link L2 between the WTRU 210 and the MAP 202 seems more attractive, (in terms of signal-to-noise ratio (SNR), estimated achievable transmission rate, estimate single-link throughput, channel occupancy, or the like), than the radio link L3 between the WTRU 210 and the MAP 203. In the prior art, since the WTRU 210 has no means of knowing that associating with the MAP 203 will result in a better throughput than associating with the MAP 202, the WTRU 210 may end up with a less favorable MAP.
Accordingly, it is desirable to have a method and apparatus for enabling a WTRU to intelligently associate with a MAP in a mesh network.